United States Patent [I9J
`Ge et aI.
`
`I ~IIIII.IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
`USOO5402t43A
`5,402,143
`(II] Patent Number:
`[45J Date of Patent:
`Mar. 28, 1995
`
`[7,J
`
`[54J COWR FLUORESCENT UQUID CRYSTAL
`DISPLAY
`Inventors: Shichao Ge. Santa Clara; J emm
`LiaDg. San Jose, both of Calif.
`[73J Assignee: Paaocorp Display Systems,
`Sunnyvale, Calif.
`
`[2IJ Appl. No.: ,.. ....
`
`[22J Filed:
`
`May 18, 1994
`
`Rellted U.s. AppHcation DatI
`[63] Continuation of Ser. No. 812,730. Dec. 23, 1991, aban(cid:173)
`doo<d.
`Int. 0 ,6 ................. .
`{51]
`[52] U.s. O ............. .
`
`Field or Sean;:h .
`
`... ..... ............ G09G 3/36
`. .......... 345/ 102; 34SnS;
`345/5
`..... 345/4, S, 74. n, 102
`Refermca Cited
`U.S. PATENT DOCUMENTS
`
`(58]
`
`[56]
`
`3,783, 184 1/ 1974
`4,593,977 6/1986
`4,610,507 9/1986
`4,610,~ 9/1986
`4,752,771 6/1988
`4,763,187 81l 'JI\S
`4,767,186 8/1988
`4,nJ,88S 9/1988
`4,791,415 1211988
`4,832,461 Vl989
`4,901,140 2/1990
`4,907,862 3/1990
`4,gSa,911 9/1990
`S,093,652 3/1992
`S,12I,233 6/1992
`5,12&,782 1/1992
`5,142,388 8/1992
`5,157,524 ]0/1992
`
`Emsloff .
`Takamatsu &::1 al.
`Kamamori et aI.
`Sorimachi el al.
`Katogi et aI.
`BibetUn .
`Bradley, J r. el al.
`Uclw"a et aI.
`Takahashi .
`Yamagishi 0::1 aI.
`Lang el aI ..
`Suntob .
`BeiswlI!nger et aI.
`Bull 0::1 aI ................. .
`Spencer 0::1 aI.
`Wood
`Watanabe et aI ........ .
`Dijon el aI.
`
`.......... J45nS
`
`.... }45j]02
`>IW184
`.... 345/ ]02
`.. 340nSI
`. ........ }4S/89
`
`FOREIGN PATENT DOCUMENTS
`0261896 3/1988 European Pal. OfT ..
`0369730 SI]990 European Pal. Off ..
`6]·224256 10/]986 Japan .
`211 2]45 4/1990 Japan.
`
`2136186 9/1984 Uniled Kingdom .
`W08802129 3/1988 WIPO.
`WOO1 / 10223 7/1991 WIPO .
`
`OTHER PUBLICATIONS
`Coloray Display Corporation, "Field Emulsion Display
`Technology Review" T echnical Note #01, Oct. 1990,
`pp. 1 107.
`Hayashi, o::t aJ. "A 15- mm Trio Pitch Jumbotron Dc·
`vicc", SlD 89 Digest, pp. 98-101.
`R esear ch Disclosure, Jan. 199 1, entitled "Cathodolu·
`minescent Backlight for Liquid Crystal Displa~", p.
`74.
`"Gray-Scale Ferroelectric Liquid C r ystal Devices," b y
`Annitage, LiqUid Crystal Displays and Applications,
`SPIE vol. 1257;pp. 11&-124 (1990) .
`"A Passive-Matrix-Addressed Ferroelectric Uquid(cid:173)
`Crystal Video Display," by Hartmann et aI.,Proceedings
`o/ the SID, vol. 32/2:pp. 115-120 (1991) .
`Primary Examiner- J effery Brier
`Attorney, Agent, or Firm-Majestic, Parsons, Siebert &
`Hsue
`["J
`ABSTRACT
`An electronic fluorescent device (EFD) is used as the
`back light source for a black/white LCD. Where the
`EFD provides red, green and blue Light, the LCD dis(cid:173)
`plays multi-color o r full-color images. The Em in(cid:173)
`cludes a number of cathodes disposed in a vacuum
`chamber, an anode, phosphor strips neat the anode, and
`grid electrodes for controlling the timing of the light
`generation and sequcntia1 color addressing. The control
`s~tem may be such that the transmission rate of the
`LCD is proportional to the amplitude o f the input signal
`forming an analog system; the EFD then simply pro(cid:173)
`vides sequential red. green and blue light pulses of con(cid:173)
`stant intensity. Alternatively, selected pixels of the
`LCD may be addressed digitally to be either on or ofT,
`and the intensities of the red, green and blue pulses
`provided by the EFD are varied. In both in stances, full
`scale gray tone monochromatic, multi-color or full·
`color images caD be achi eved.
`
`40 Claims, 12 Dra"lng ShetU
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`Page 1 of 24
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`U.S. Patent
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`Mar. 28, 1995
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`U.S. Patent
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`u.s. Patent
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`Mar. 28, 1995
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`Sheet 12 of 12
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`
`1
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`5,402,143
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`2
`further reduces the light transmitting portion of the
`pixel and is undesirable. For a display with many pixels,
`the red\.ICtion in IU"" i$ con.siderable. For example, for a
`480 by 240 pixel display. 480x 240 X 1 transistors must
`be used even without any redunduncy in transistors. If
`rc:dundunt transistors are included, such as by using two
`transistors for each color in a pixel, 480 X 240X 3 X 2
`transistors must be used.
`For the reasons above, it is difficult to use the above(cid:173)
`described conventional designs to acbieve efficient
`color LCD displays of high brightness, good color and
`high resolution. This is particularly the case for large
`displays. It is therefore desirable to provide an alterna(cid:173)
`tive design for color LCD displays which are inexpen(cid:173)
`sive and where the above-described difficuhies are
`avoided or alleviated.
`
`COWR FLUORESCENT UQUID CRYSTAL
`DISPLAY
`
`This is a continuation ofapplication Su. No. 812,730.
`filed Dec. 23, 1991, now abandoned.
`BACKGROUND OF THE INVENTION
`This invention relates in general to an efficient dis(cid:173)
`play device capable of displaying monocbromatic, mul- 10
`ti-color and full-color images of high brightness and
`resolution. Specifically, the invention relates to a liquid
`crystal device (LCD) without color mten, where the
`LCD is illuminated by a back lighting source, which is
`an electronic fluorescent source emitting monochro- 15
`matic light or light of multiple colors. such as tbe three
`primary colors of red, blue and green.
`SUMMARY OF mE INVENTION
`LCOs are one of the most widely used type of de(cid:173)
`vices. However, most of tbe LeOs used today are
`Thls invention is based on the observation that the
`monochromatic. While multi-color and
`full-color 20 above-described difficullies of conventional color
`LeOs have been proposed, their development has been
`LCOs can be alleviated or avoided altogether by using
`an electronic fluorescent device (Em) as the back light
`hindered by a number of technical difficulties. In most
`of the multi-color and full-color LCDs proposed, a bact
`source in place of a white light source with filters. The
`light S()urce is employed. However, in most cases, the
`flat panel color display apparatus of this invention com-
`back light source employed is white light. Therefore, to 25 prises a layer of liquid c~tal material, means for ad-
`produced composite images of different color, red, blue
`dressing locations on said layer to cause said layer to
`and green ft]ter arrays have been used. For each pillel,
`modulate the intensity of light transmitted through said
`the white light directed towards a portion of the pixel is
`layer at selected locations, and a back light source for
`mtered to permit only red light to pass, and white ligbt
`supplying light towards the liquid crystal layer. The
`directed toward another portion of the same piAtl is 30 back light source comprises a housing defming therein a
`ftltered to permit only blue light to pass and the white
`vacuum chamber, a plurtlity of cathodes disposed in th~
`light directed towards the remaining portion is filtered
`chamber, means for causing the cathodes to emit elec-
`to permit only green light to pass. Thus only a small
`trons and an anode in the chamber. The source further
`includes control means in the chamber for causing the
`part of the energy of the white light is transmitted
`through the LCD. If relatively pure red, blue and green 35 electrons emitted by the cathodes to travel towards the
`light is desired, the ftIters employed must have narrow
`anode at selected locations. and means disposed in the
`pass bands, so that the percentage of the energy of the
`cbamber at or near the anode and responsive to said
`white light utilized is further reduced. Alternatively, if
`electrons- for generating and directing light toward the
`a brighter display is desired, tbe user may have to com-
`layer of liquid crystal material.
`promise on the color quality and utiliz.e red, blue and 40
`gre.en filten with bf04der pass bands.
`LCD cells respond slowly to voltages applied across
`them. Typically, when scanning voltages are first ap(cid:173)
`plied to a LCD cell, the cell has low transmission rate.
`The transmission rate rises slowly during tbe $C8IlIIing 45
`cycle so that a low percentage of light is passed by the
`red. blue and green filters and transmitted. through the
`LCD cells during the scanning cycle. This is a notable
`drawback of passive matrix type LCD color displays,
`where no drivers are used contiguous to the LCD cells SO
`for driving the cells.
`To improve display brightness, active matrix LCD
`cells are proposed by adding at least three thin film
`transistors for each LCD cell or pixel for accelerating
`the turning on and off of the three portions of the cell or 55
`pixel for light transmission of the three different colors.
`Such transistors, however, are opaque and occupy a
`significant area of the LCD cell. In other words. what(cid:173)
`ever the d~gner may have gained by increasing the
`transmission rate:, the designer will lose at least part of 60
`the advantage because of the reductiOIl of the area of
`the cell that actually transmits light.
`A further complication in the active matrix LCD
`type displays is in manufacturing. Thus if a thin film
`transistor in one of the LCD pixels or cells is defective, 65
`the entire display is useless and must be discarded. Be(cid:173)
`cause: of yield problems. redundant tnms.istors are im(cid:173)
`plemented. However, adding more thin mm transistors
`
`BRIEF DESCRIPTION Of !HE ORA WINGS
`FIG. 1 is a cross-sectional view of a portion of a
`passive matrix electronic fluorescent LCD to illustrate
`an embodiment of the invention.
`FlO. 2 is a block diagram of an electronic control
`system for applying various voltages and signals to the
`de vice of FIG. I to illustrate the invention .
`FIG. 3 is a schematic view of a portion of an active
`matrix conventional LCD device.
`FIG. 4 is a schematic view of a portion of an active
`matrix electronic fluorescent LCD device to illustrate
`an embodiment of the invention.
`FIG. 5 is a cross-sectional view of an electronic fluo(cid:173)
`rescent LCD device to illustrate further features of the
`invention.
`FIG. fi is a schematic view shOwing electrical con(cid:173)
`oections between the grid electrodes of an EFD for
`addressing different phosphor strips that correspond to
`M pixel arrays to illustrate the invention.
`FIG. 7 is a cross-sectional view of a portion of an
`electronic fluorescent LCD device employing cone(cid:173)
`shaped. field electron emitting cathode structures to
`illustrate another embodiment of the invention.
`FIG. B is a perspective view ofthe top surfaces of the
`gates and tbe tip portions of the cathodes of the elec(cid:173)
`tronic fluorescent LCD device of FIG. 7.
`FIG. 9 is a cross-sectiona1 view of a portion of the
`electronic fluorescent LCD device of FIGS. 7 and B.
`
`Page 14 of 24
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`5,402,143
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`3
`FlG. 10 is a timinS diagram illustrating the addressing
`and conlrol signals applied by an address and control
`system such as that of FIG. 2 to an analog gradation
`electronic fluorescent LCD device to illustrate the in-
`vention.
`FIG. 11 is a block diagram o( a control system for
`operating an analog gray scale electronic fluorescent
`LCD to ilIustrale the invention.
`FIG. 12 is a timing diag:ram of control signals and the
`transmittance of the LCD to illustrate a digitaJ gray
`scale electronic fluorescent LCD 10 illustrate the inven-
`tico.
`FlG. 13 is a timing diagram of control signals for
`electronic fluorescent LCD devtce to illwtrale in more
`detail the scheme of flO . 12 for generaling digital gray
`IOoe values.
`FIG. 14 is a timing diagram of control signals to
`illustrate alternative schemes to tbat of FIGS. 12. 13 for
`implementing digital gray toDe values.
`FIG. 15 is a schematic circuit diagram illustrating a 20
`control circuit for generating the control signals of
`FIGS. 12. 13.
`FIG. 16 is a schematic view of a portion o( an elec(cid:173)
`tronic fluorescent LCD device to illustrate an aspect of
`the invention for reducing cf'OS5talk.
`FIG. 17 is a schematic view illustrating the effect of
`turning 01T early the data-pulse to the electronic fluores·
`cent device in reducing crosstalk..
`FIG. 18 is a c rou-sectional view of an electronic
`nuorescent LCD to illustrate a mosaic type display.
`
`4
`similarly elongated and form a substantially coplanar
`amy of preferably sub5.Wlti&l.ly parallel e1ectrodes.
`11111$ each column elcctrode overlap$ each of the row
`electrodes. where the overlapping square or rectangular
`area of a row electrode and a column e1cctrode defmes
`a pixel of LCD 32 and of the EFLCD 30. Thus the
`pixels of EFLCD form an array with linear rows of
`pixels parallel to ami .Iigued with the array of row
`electrodes 54. While ill the description above in refer-
`10 ence to FIG. I. the row electrodes 54 are the scanning
`electrodes. it will be understood that the column elec(cid:173)
`trodes S2 may be used for scanning. in which case tbe
`array of corresponding pixels will be scanned column
`by columll instead. All such variations are within the
`1:5 scope of the inventiOll. As described in detail below.
`scanning sipals are applied to the row electrodes 54
`and data signals are applied to tbe column e1ectrodes 52
`where the scanning and data signals rogctber control
`the transmission rate of each pixel of the light passing
`therethrough. The above-docribc:d structure and oper(cid:173)
`ation of LCD 32 is thaI of a passive, simple matrix type
`conventional LCD.
`In tbe embodimenl of FIG. 1. EFD 34 is a full-oolor
`electronic fluorescent back lighl (EFBL) source wbich
`provides red, green and blue lumin~nce . EFO 34
`comprises a back plate 72 and a face plate 74. anode 76
`on the internal surface of back plate 72, and elo ngated
`red. green and blue primary colo.- phosphor strips 78 on
`)() tbe anode. Back plate 72, face plate 74 and side plate 82
`fonn a bousing which enclose therein • sealed chamber-
`84 which is ev.acuated. Disposed in vacuum chamber 84
`DETAILED DESCRIPTION OF THE
`is a first set of grid electrode3 86 and a second group of
`PREFERRED EMBODIMENT
`flO. 1 is a cross-sectK>nai view of the portion of an
`grid electrodes 88. and calhodes 90.
`Filaments of cathodes 90 may be the type th.at are
`electronic fluorescent LCD (EFLCO) to illustrate one 35
`provided with direct heu.ting oxide coatings. In the
`embodiment of the invention where the LCD dev1ec
`therein is the passive type with no devices contiguous to
`embodiment of FIG. I, when nlamcnU 90 arc heated by
`the LCD puels or cells for driving the: cells. As sbown
`means of rated beating voltage, the fi]amenu emit elec-
`trems. A voltase difference is applied between the cath-
`in FlO. I, EFLCD 30 comprises the passive matrix
`LCD 32 and an electronic fluorescent device (EFD) 34. 40 odes 90 and anode 76 50 that the dectrons emitted by
`LCD 32 is a black/while LCD without color mien and
`the cathodes will travel towards the anode. When these
`EFD 34 emits substantially monochromatic light or
`electrons impinge on tbe phosphor strips 78, the phos-
`phor strips will re3pond by generating red, green or
`light of differenl colors as a back light source. The
`addressing and control syslems (or addressing and con-
`blue light. The surface of the anode facing the LCD 32
`is highly light reflective to increase the efficiency of the
`trolling LCD 32 and EFD 34 are synchronized so that, 4:5
`where EFD emits light of different colors, the combina-
`device.
`tion of the devices of 32 and 34 turn an originally
`Three types of pbosphor strips are employed: the flnt
`black/white LCD 32 into a high brightness Krul efficient
`type geDerales red light,. the second type green light,
`multi-color Of' full-color display with good color. While
`and the third type: blue light, in response to electrons.
`in the preferred embodiment. EFO 34 emits light of SO The light generated by phosphor strips 78 are transmit-
`multiple colors, such as red, blue and green light, it will
`ted across chamber 84 through face plate 74 to the LCD
`be undel$tood that EFD 34 may also be monachro-
`32 When selected pixels of LCD 32 are rendered light
`transmitting. the light emitted by the pbosphor strips 78
`matico
`will be transmined through such pixels 10 display im.-
`In FIG. 1, LCD 32 may be a black and white digital
`LCD, o r a single-matrix or multi-matrix passive LCD, " age3 o( the required coloR. To achieve uniform back
`or an active matrix LCD with thin film transistors
`lighting intensity. it is preferable 10 emplo)' denser oar-
`(TFT) but can also be a digital modulation or analog
`row arrays of phosphor strips 78 where the widlh ohhe
`modulation LCD. When combined with an electronic
`individual strips are smaIl compared to the widths or
`fluorescen t bad: lighting source 34, the combination
`electrodes 52 or 54 of LCD 32. The outside surface
`<:aD achieve many different display funchoDS.
`60 and/or inside surface (thaI is, the surface closer and
`LCD 32 comprises poJarizen 41, .... face plate 46 and
`adjacent to vacuum chamber 84) are diffLLSion surfaces
`back plate 48, and two groups of preferably mutually
`to increase the uniformity of the back lighting intensily.
`perpe:ndKlu1ar)t, Y electrodn.54. 52 resper::tively. a layer
`To provide suppon to the face and back plates 74. 72
`against atmospheric prCS5ure, spacers 92 are employed
`of liquid crystal material 56. and side sealing walls 58.
`As in conventional LCOs, the row or x electrodes are 63 to provide sufficient mechanical strength to the bousing
`elongated and form a substantially coplanar array
`of EFD 34 and so that the race and back plates can be
`where the electrodes are preferably substantially para!_
`lUde TCbtively thin even when lhey h.ave large surface
`lei to oDC another. The y or column electrodes 52 are
`areas. In such manner, a fl.at panel color electronic fluo-
`
`Page 15 of 24
`
`

`
`5,402,l43
`
`5
`rescent LCD 30 is provided where the total thic:kneu of
`device JO may be Jess lhan 2 em.
`Preferably, to reduce any dark areas that may be:
`visible on the display screen, spacers 92 are elo ngated
`memben with a wcdse-shaped cross-section with a $
`thinner side 920 facing LCD 32 as shown in FIG. 1. The
`two slanting side surfaces 92b arc highly reflective dif.
`fusing surfaces in o rder 10 renee! light impinling
`thereon towards the LCD 32, in order to further reduce
`any dark areas that may be visible throu&h LCD 32, in
`order to achieve unifoml intensity back lighting. Prefer(cid:173)
`ably, 11$ shown in FIG. 1. layer M is a transparCD t con(cid:173)
`ductive fllm on the internal surface of racc plate 74;
`conductive film M reduces any effect of extraneous
`electric and magnetic fields on thc EFBL 34.
`LCD device 31 is addressed in a conventional man(cid:173)
`ner. Typically. row electrodes 54 and the correspond(cid:173)
`ing rows of pixels arc scanned one al a time and sequen(cid:173)
`tially, for example, rrom the top row towards the bot(cid:173)
`tom row, until the bottom row is reached at which time 20
`the top to bottom scanning process is repeated. At the
`same time, data signals are p rovided to column elec(cid:173)
`trodes 52, where the scanning sigrWs to row electrodes
`54 and data signals to column electrodes .52 together
`would determine: whether any particlliar piKc:I is ren- 25
`derc:d light transmining or not IS well as determining
`the: transmission rate of the: puel as is known to those:
`skilled in the art. For this reason, the detailed working
`mechanism of LCD 32 will not be elaborated here.
`Since the LCD 30 is typically scanned one row e lte- 30
`trode or one column electrode at a time, fOr improved
`errlCiency, it may be desirable to provide backlighting
`only to the portt<ln of the LCD which is being scanned.
`For this reason, preferably the elong ated phosphor
`strips 78 are arranged substantially parallel 10 the array 35
`of electrodes being scanned; in the case of FIG. J, strips
`78 are arranged parallel to the array of row electrodes
`54 which are scanned one at a time from top to bottom.
`In FIG. I, f(K' eumple, during operation of the device,
`the left edge of device 30 is rotated to become the top .a
`surface so that the leftmost row electrode 54 becomes
`the top electrode and the scanning proceeds from the
`top electrode downwards.
`For improved efficiency, during the scanning of the
`topmost fo ur o r five row electrodes 54 ( that is, the four 4S
`or five near side wall 58, all shown in FIG. 1), only the
`cathodes 90 and the grid electrodes between the side
`plau: 82 and spaur 92 need lO be used fOl' generating
`back tight. Thus the plurality of spacers 91 may be
`p rovided in chamber 84 to divide the chamber into a SO
`number of subchambel$. A control means described in
`detail below is then used for applying different voltages
`to the cathodes and the grid electrodes to cause the
`cathodes and grid e lectrodes in each subchamber lO
`generate electrons so that only the phosphor strips dis- "
`pos.cd within the subchamber will emit light towards
`through the row electrodes 54 which are being SoCanned
`at the same time. In this manner, the opentK>o o f device
`30 is made more efficient. Moreover, tbe phosphor
`strips are arranged to alternate periodically in the repet· 60
`itive order (e.g. R, G, 8, R, G, 8 , ... ) as illustnted in
`the figures.
`FIG. 2 is a block diagram o f a system 100 iIluslntina
`one embodiment of the addressing and control system
`of the EFLCD device of this inventton. For simplicity, U
`identical componenu. in the different figures of this
`application are referred to by the ~e numerals. The
`L C D 32 may be controlled via analog signals where the
`
`6
`transmission rates of a number of selected pixels in a
`row of piu,1s being scanned are proponional to the
`amplitudes o f analog input sia:nals. In such event, the
`LCD column drivers 101 are controlled directly by the
`lUIa10g input to generate the analog data signals applied
`to the column electrodes of L CD 32. In such case, the
`EF8L 34 w ould simply provide constant amplitude and
`fixed width red, ,reen and blue pulses in synchronism
`with the LCD addressing to provide red, green and blue
`10 light of different gray lOnes that are
`transmitted
`thro u.gh the LCD 32. Such analog addressing will be
`dcscnbcd in more detail below in rdercncc: to FIGS. 10
`and 11.
`Alte rnatively, each scanning cycle will be d ivided
`is into three, six, nine, twelve, ... ,(increasing as multiples
`of three) segments, and durina: each segment of the
`scanning cycle, each pixel in the pixel row scanned is
`either entirely closed to light t.ransmission or fu.lly
`turned on for maximum light transmission_ In synchro(cid:173)
`nism therewith, the display control unit 104 then gener(cid:173)
`ates a fixed sequential pattern of voltage plllses applied
`to the EFBL 34 fo r generating a rued panero of vary(cid:173)
`ing intensities of red, green and blue light pulses. Each
`segment of the scanning cycle of the LC D 32 corre(cid:173)
`sponds 10 each o f the red, green and blue light puIsc:s.
`By selecting to pass o r not to pass each of such pubes
`d uring each segment of the scanning cycle, different
`gray tone red, green and blue light transmission thro ugh
`the LCD 32 is accomplished. Such digital operation
`will be described below in reference to FIGS. 12- 15.
`In reference to FlO. 2, display control unit t04 gener(cid:173)
`ates scanning pulses for driving the L CD row driven
`106 which in tum generate the scanning pulses fo r scan·
`ning the rows of electrodes LCD 32. D isplay control
`unit 1M also generates the RG B data pulses which are
`fed to EFBL driven 108 through RGB scanning unit
`110. Where the .scanning cycle is to be divided into a
`number of scanning segments. the input signal fed at 101
`is convened by AID con ven er 112 into a sequence o f
`bits fOl' controlling whether the pixels in the scanned
`pixel row should be o n o r o ff. Such sequence o f bits are
`stored in the video memory 114 and are then fed to
`LCD column d riven 102 for controlling turning on and
`off the pixels in the scanned pixel row in LCD 31. The
`operation of AD convener 112 and memory 114 are
`controlled by display control unit 104. The display
`control unit 104 also generates a stream of digital signals
`lo ROB scanning unit 110 and E FBL drivers 108 for
`generating Cued patterns of voltaie signals for applica(cid:173)
`rion to the cathodes and grid electrodcs of the EFBL 34
`fOf generating a selected one o r a number of rued pat-
`terns o f red, green and blue light pulses.
`In the embodiment of FIG. I, LCD 32 is a passive
`matrix device with no active devices implemented adja(cid:173)
`cent lo the LCD layer 36 for driving the LCD pixels.
`As indicated above, passive matrix LC D devices are
`slow. For this reason, active matrix L CD devices have
`been proposed such as those iIlustr.ted in FIG. l . As
`shown in FIG. 3, ISO is a schematic view of a portion of
`a convenrional active matrix LCD where thin mm tnm_
`liston 152 are implemented contiguous lo the pixels for
`driving the pixels. As can be seen fro m FlG. 3, since
`conventional color LCD devices employ filters whic h
`permit only one of either red, green or blue light to pass,
`these ruters cannot overlap so that each individual pixel
`must comprise subpiIels each d esignated to transmit
`only fcd, green o r blue light. For this reason, in order to
`produce a full range o f multi-color or fulJ.co!or images,
`
`Page 16 of 24
`
`

`
`5,402,143
`
`lrid electrodes in the ftnt set * that are aligned with
`
`7
`8
`each piKI must comprise al least three subpucls 154.
`heating voltage from unit 104 through EFBL drivers
`108 10 generate electrons 202.
`These subpuds are typically sequentially addressed ODe:
`When red light is to be generated, appropriacc volt-
`row al a time at a relatively high frequency so that, to
`ages are then applied to the rltSt set of grid electrodes
`the eyes of an obIerver, all three colors an: stably dis-
`204 in FIG. 5 10 thereby cause electrons 102 to be di-
`played. Where the subpixds are suffICiently small, the
`red, green and blue subpixcls wiD appear to merge to
`reeled only towards the phosphor Strips R, and IlOI
`towards the phosphoT strips G, B. During the time
`give the uniform color of a particular color with Iray
`interval dllrins which green light is to be emitted by the
`lODe$.
`EPD ZOO, the voltagcs applied to the grid electrodes
`In FlO. 3, the x bus carries scanning signals for scan.
`rung rows of subpixcls and the y bus carries data signals 10 204 should be such thlt the electrons should be directed
`only toward" the phosphor stripslabcled G . The same is
`which together with the scanning signals modulate tbe
`transmission rate of each pixel. AI can be observed from
`true during the time interval for generating blue ligbt,
`FIG. 3, in order to address the three: subpilleb of each
`dw'ing which the electrons are to be directed only
`pixel individually, a significant percentage of the dis-
`towards the pbosphor strips B. Typically, this can be
`play area is occupied by the x and y buses. H thin film IS achieved by applying a more p:>Sitive voltage to the
`transiston such as ltanSiston 152 are employed to speed
`up the LCD, additional areas of the LCD display screen
`and correspond te:' the appropriate set of rh;osph~ strips
`and a ~ore negauve voltage to the ~nlJlg grid e1ec-
`will be occupied by these transistors, thereby further
`trodes In the. flfSt set .. Thus '-! sh?wn In FlG. 5, e~h
`reducing the percentage of the display screen which can
`transmit light. AI Doted above. because of yield prob- 20 phosphor stop ~ ahgned w;'-th It and corTcspondmg
`!ems. sometimes two thin film transittors are employed
`thereto, three grid e1e:cuodcs m the fint 5Ct lOol, where
`the three correspo~mg electrodes are connected to-
`for each subpixel; in such event, even a larger percent-
`gether ~y an electri~ co~uctor 206 so that when ~e
`of the area of LCD d ' La screen is occupied by
`a
`appropnau voltage IS .applied to one ~f the three gnd
`a:que circuit elements. ~r ~e above reasons, con.
`vCDtional color LCD docs not provide images of good lS electrodcs, all three g~d electrodes will be at the .same
`ffi' t
`b 'ghtn
`d "
`voltage. Such connection renders the voltage uniform
`lS ute ~CI~ .
`n
`.
`.
`ess. an
`betWeeII the three grid electrodes corresponding to a
`FI~. 41$ a schcmab~ VIe,,:, of a pomc:m. of an .actlVe
`phosphor strip and improves the uniformity of the light
`matm; color LCD dev~ to ilI~trate ~ mv~nbon. In
`emission of the EFD 100 and tberefore the overall qual-
`co:nt~t to .the conveDbonaJ deVice 150, III devtce 170 of 30 ity of the display using the EFD. So ali&ning the three
`~ m,vennon, no color. fi]ten: are employed and ~h corresponding grid dectrodes with their oorresponding
`pixel lS used .to traruimlt ~I colors of t~e back light
`phosphor strip and applying appropriate voll.a8es re.
`duct the number of dectrons directed towards other
`source. Thus If tbe back light $Durce emus red, green
`and bl~ light. each pi